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       Jifty::Manual::Models - Managing your datastore


       The idea behind a model is to give the user a database-independent way of defining how the
       data looks alike and how different parts of the data relate to each other. In database
       terms, you might think of a schema definition.

       Besides the pure definition of a model, creation, updating and lookup of data are also
       possible in a comfortable way.

   Creating a model
       Every model consists of two classes: AppName::Model::ModelName and
       AppName::Model::ModelName::Schema. Behind the scenes, a class named
       AppName::Model::ModelNameCollection is created by Jifty::ClassLoader.

       A simple model to store just one line of text might look like this:

           use strict;
           use warnings;

           package MyApp::Model::TextLine;
           use Jifty::DBI::Schema;

           use MyApp::Record schema {
               column 'textline';

           # Your model-specific methods go here.


       To create the database schema for a model inside an application you could simply run:

           jifty model --name TextLine

       from inside your application's directory and Jifty will create exactly this class
       structure for you (minus the column line, to be precise).

       Schema definition language

       Creating a model has important side effects:

       · correctly type your data inside the data-store

       · let Jifty create (and update) your database schema for you

       · tell Jifty the behaviour in terms of form display

       · allow to work with multiple records (referred to as Collections) without effort

       To get all these things done, Jifty allows one to describe the schema definition in a
       simply comprehensible but powerful syntax that looks more like written text than a
       programming language. The schema definition is made inside the "MyApp::Model::XXX::Schema"
       package and every single column to get created starts with the word "column" followed by
       the column's name.

       A simple definition could look like this:

           column name =>
               type is 'text',
               label is 'Name',
               render as 'Text',
               since '0.0.1';

       The following BNF shows the full syntax supported (omitting non-terminals that are self-
       explanatory to perl-developers):

           schema_definition ::= column_definition+

           column_definition ::= 'column' string_columnname '=>'
                                 column_info [ ',' column_info ]+ ';'

           column_info ::= 'type' 'is' string
              | 'label' 'is' string
              | 'render_as' string
              | 'render' 'as' string
              | 'hints' 'is' string
              | 'refers_to' class_name 'by' string_columnname
              | 'default' 'is' string
              | 'literal' 'is' string
              | 'validator' 'is' subroutine_reference
              | 'immutable'
              | 'unreadable'
              | 'display_length' 'is' number
              | 'max_length' 'is' number
              | 'mandatory'
              | 'not_null'
              | 'distinct'
              | 'virtual'
              | 'computed'
              | 'sort_order' 'is' number
              | 'input_filters' 'are' string_classname
              | 'output_filters' 'are' string_classname
              | 'filters' 'are' string_classname
              | 'since' string_version_number
              | 'valid_values' 'are' array_of_valid_values
              | 'valid' 'are' array_of_valid_values
              | 'hints' 'are' string

           * 'is', 'by', 'on', 'as' and 'are' are fill-words that may get omitted.

       For a full description of each parameter's meaning, look at Jifty::DBI::Schema.


       Every time you run the jifty utility with "schema" as an argument, Jifty will keep track
       on what it has done for you. To get that done, the version-number being stored in your
       application's config file "etc/config.yml" under the key named "framework/Database/Verson"
       is matched against your schema definition.

       To force an update of your schema, simple create a new version number in your config file
       and modify your schema definition by using exactly this version number for every modified
       entry. After running

           jifty schema --setup

       your database structure will be in sync to your schema definition.  See
       Jifty::Manual::Upgrading for more information on model upgrading.

   Testing a model
       After having created a schema, you might use the ADMINISTRATION Menu entry in Jifty's web
       view (i.e. the "pony") to browse through your models and add, edit or delete records in
       your database.

   The classes behind a model
       · MyApp::Model::Xxx

         This is the model-class you created to access individual records of your desired type.
         You will directly deal with objects of this class.

       · MyApp::Record

         All records of "MyApp::Model::Xxx" will have this class as their base class. Usually,
         this class will be automatically created by Jifty::ClassLoader for you. But, if you want
         to automatically enable all your records to do something, you will have a chance to do
         so by manually creating this class.

       · Jifty::Record

         This is the super-class of "MyApp::Record". Inside this class, loading of records as
         well as the checking of user capabilities is done before going one level down to the
         database layer.

       · Jifty::DBI::Record

         This is the lowest-level class that the database stack provides. It directly deals with
         the underlying database.

       · App::Model::XxxCollection

         As the name applies, a collection is a set of typically more than one record. Every
         collection of this class consists of multiple "App::Model::Xxx" objects that can get
         retrieved from your data-store without explicit SQL statements, ordered by any criteria
         you give, paged in the fashion you like, and iterated sequentially or accessed at random

       · App::Collection

         Every collection of your schemata will have this class as its base. Usually this class
         is automatically created by Jifty::ClassLoader. If you intend to create new features for
         all of your collection this will be your chance to do.

       · Jifty::Collection

         This is the base class of an "App::Collection", managing user capabilities on records it
         will keep track of.

       · Jifty::DBI::Collection

         This is the lowest-level base class that directly manages the access to the underlying

   Working with a single record
       Working with a single record means working with objects of classes like
       "MyApp::Model::Xxx". The typical creation and usage of a single record is:

           # create an object to allow data access
           my $object = new MyApp::Model::Xxx;

           # either create a representation in the DB
           $object->create(column => 'value', ...);

           # or load the data from DB somehow
           $object->load($id); # by a matching ID
           $object->load_by_cols(column => 'value', other_column => 'secondvalue');

           # try to load and if failed, create a record
           $object->load_or_create(column => 'value');

           # get the record's ID in the database
           # results in 'undef' if record is not valid (which usually means not found)
           my $id = $object->id;

           # delete the record from the database

       To access data stored in different columns of a record you may use some of the
       automagically created methods on the object:

           # read some column named 'colname'
           my $value = $object->colname;

           # write some value to a column named 'colname'

           # get all columns in a single hash (not a reference!)
           my %record = $object->as_hash;

       Especially, when writing to a record, you need not worry about how to write back the data
       to the database, the object will manage this step on its own.

   Working with multiple records
       Working with more than one record of the same object-class brings collections into the
       game. Usually, a collection you deal with is of a type that conforms to your model name,
       "MyApp::Model::XxxCollection" and usually holds records of class "MyApp::Model::Xxx". You
       typically use a collection like this:

           # create a collection object
           my $collection = new MyApp::Model::XxxCollection;

           # get all items of the model into the collection

           # or restrict items to match some condition
           $collection->limit(column => 'colname', operator => '=', value => 42);

           # bring the items into some sorting order
           $collection->order_by(column => 'colname');

           # if neccesarry, directly jump to some record from the set


           # iterate through the result set
           while (my $record = $collection->next) {
                 # do something with $record

           # directly access the first or last item
           # be careful: this will set the current position also!
           my $first = $collection->first;
           my $last  = $collection->last;

           # get back an array-ref containing all items
           my $records = $collection->items_array_ref;

       Some options provided by "limit"

       In order to construct more complex restrictions the "limit" method may get called more
       than once, specifying one single condition with each call.

       Every use of "limit" constructs either a clause or a subclause.  A subclause is built
       either if the "subclause" attribute is used or a column is used repeatedly.

       Every clause is built up by combining its subclauses (if any) using the "entry_aggregator"
       operator (whose default is OR) as a combining operator. Clauses are then "AND"ed together
       to yield the final restriction that is finally used to retrieve the records in question.

       The "operator" (whose default is '=') can be any legal SQL operator like "=", "<=", ">=",
       "!=", "LIKE", "IS", "IS NOT" as well as some convenience operators that silently use
       "LIKE" with properly set wildcards ("MATCHES", "STARTSWITH" or "ENDSWITH").

           # combining restrictions with "AND"
           # note that "AND" is implicit here unless a column name is repeated
           $collection->limit(column => 'col1', value => '...');
           $collection->limit(column => 'col2', value => '...');

           # combining restrictions with "OR"
           # note that the 'subclause' has the same value
           $collection->limit(column => 'col1', value => '...',
                              entry_aggregator => 'OR', # is already default
                              subclause => 'some_id');
           $collection->limit(column => 'col2', value => '...',
                              entry_aggregator => 'OR', # is already default
                              subclause => 'some_id');

       For debugging purposes, you might want to examine the SQL statement generated behind the

           warn $collection->build_select_query;

       See Jifty::DBI::Collection about more ways or ordering and limiting collections.

   Action - Model relationship
       When writing templates you often simply access some record from a model and want to
       operate on this very record by modifying it or you might want to add a new record of some
       type. To do this, our faithful Jifty::ClassLoader will create classes named
       "MyApp::Action::CreateXxx", "MyApp::Action::UpdateXxx" or "MyApp::Action::DeleteXxx" for
       you. This enables you to write a template to operate on a single record like this:

           my $id = some_value_obtained_somehow;
           my $record = new MyApp::Model::Xxx;

           my $action = Jifty->web->new_action(class   => 'UpdateXxx',
                                               moniker => 'mymoniker',
                                               record  => $record);
           <% $action->form_field('colname') %>
           <% Jifty->web->link(label  => 'Update',
                               submit => $action,
                               ... ) %>

       The elegant thing around here is that you could write the class name of your action-class
       simply as "UpdateXxx" instead of the full package name "MyApp::Action::UpdateXxx" and
       there is no need to write a repeating update procedure for every record class that comes
       along.  DRY - don't repeat yourself :-)


       Jifty::Record, Jifty::DBI::Record, Jifty::Collection, Jifty::DBI::Collection,
       Jifty::Manual::Actions, Jifty::Manual::Tutorial